1. Technical Field
The embodiments herein generally relate to mobile television (TV) technology, and, more particularly, to the transmission of and switching between television channels.
2. Description of the Related Art
Handheld devices with integrated digital television access are a relatively new phenomenon. Such technology has traditionally been limited by size, power consumption, and most importantly performance. Poor performance of such devices has typically been the result of the constantly changing receiver environment. More particularly, the quality of the received signal is affected by the device's ability to manage adjacent-channel rejection, low signal-to-noise ratios, and Doppler compensation, among other factors.
Digital Video Broadcasting-Handheld (DVB-H) is the specification for bringing broadcast services to handheld receivers, and was formally adopted as an ETSI (European Telecommunications Standards Institute) standard in November 2004. More specifically, DVB-H is a terrestrial digital TV standard that tends to consume less power than its predecessor, the Digital Video Broadcasting-Terrestrial (DVB-T) standard, and generally allows the receiver to move freely while receiving the signal transmission, thereby making it ideal for cellular phones and other mobile devices to receive digital TV broadcasting over the digiTV network, and hence without having to use cellular telephone networks.
In mobile TV systems such as DVB-H (ETSI EN 301 192), one radio frequency (RF) channel is shared among many TV channels (TV programs). Generally, these TV channels are multiplexed either in the time domain or in the frequency domain. When the TV channels are multiplexed in the time domain, each channel is given full access to the entire RF channel bandwidth for a short period of time (burst duration). After the burst is transmitted, bursts for other channels occupy the RF channel and so on. This multiplexing process is referred to as time division multiplexing (TDM). FIG. 1A illustrates an example of TDM of 15 TV channels on one RF channel. In FIG. 1, the TV channels are labeled 1, 2, 3, . . . , 15. In FIG. 1A, it is shown that each TV channel occupies the entire RF channel for 1/15 of the total time. Generally, a receiver (not shown) which is receiving only one channel (for example, channel 2) only has to be active (ON) during the periods of channel 2 bursts. In order to conserve battery consumption, such a receiver will shut off its circuits when channel 2 bursts are not occupying the RF channel. Thus, the receiver enters into a SLEEP mode. This demonstrates that TDM of TV channels can help reduce power consumption of a receiver watching a single channel.
On the other hand, this tends to cause a problem when a user desires to switch to receive another TV channel on the same RF channel. One example is shown in FIG. 1A, if a user desires to switch from channel 2 (currently viewed channel (VIEW)) to channel 3 (this process is denoted by channel UP in FIG. 1A). The worst-case scenario occurs when a user issues a command to switch to channel 3 immediately after the burst of channel 3 ends. In this case, the receiver has to wait until the next burst that belongs to channel 3 appears on the RF channel. This causes a user to wait for a given period of time denoted as the channel switching delay. Such a delay could be as long as 5 to 7 seconds in DVB-H systems, which detracts from the television viewing process as such a channel switching delay could be rather annoying to a user.
Each DVB-H burst is composed of one real-time transport control protocol (RTCP) data packet and a number of real-time transport protocol (RTP) data packets as shown in FIG. 1B. RTP is used to transmit data (e.g., audio and video) and the RTCP is used to monitor quality of service (QoS). The monitoring of QoS is very important for modern applications. In large-scale applications (e.g. (Internet Protocol Television's (IPTV)), there is an unacceptable delay between RTCP reports, which can cause QoS related problems. It is clear from FIG. 1B that the receiver starts buffering data only when the RTCP packet is received, then the receiver will have to wait for the next burst to buffer enough RTP packets to be decoded. As a result generic audio and video (A/V) reception methods spend more than two seconds (burst time) to receive playable A/V data, which is a very long time leading to long switching delay, which results in reduced user satisfaction.